1. Field of the Invention
The present invention relates to a pipe connecting structure, particularly a pipe connecting structure that connects two pipes with improved air tightness.
2. Description of the Related Art
In general, two pipes in refrigerating cycle systems for a vehicle are connected by flange blocks as shown in FIG. 1.
In detail, a flange connecting structure has a male flange block 4 of a peanut shaped cross section combined with a first pipe 2 and a female flange block 8 of a peanut shaped cross section combined with a second pipe 6 that are fastened by a bolt 10. The male flange block 4 has a protrusion 4a having a hole communicating with the first pipe 2 and the female flange block 8 has an insert portion 8a to which the protrusion 4a is inserted. A rubber sealing member 12 (O-ring) is fitted around the protrusion 4a for sealing. The bolt 10 is fixedly inserted in a hole 8b of the female flange block 8 through a through hole 4b of the male flange block 4.
In recent years, refrigerating cycle systems using an environmentally friendly natural refrigerant of Carbon dioxide (CO2) have increased because Freon gas causes environmental pollution.
A refrigerating cycle using CO2 refrigerant as a heat exchange medium is a supercritical refrigerating cycle with internal pressure exceeding a critical pressure, so that the internal pressure is a lot larger (generally, about 7 to 9 times) than refrigerating cycle systems, in the related art, using a Freon-series refrigerant. The internal temperature of the system ranges from −40° C. to 180° C.
Rubber sealing members (O-ring) used in pipe flanges of the refrigerating cycle system for vehicles in the related art cannot bear the high pressure in the refrigerating cycle system using CO2 refrigerant. Sealing members of ethylene-based (ACM) rubber is relatively high in density, so that they are short in elasticity at a cold region under extremely low temperature. Therefore, when the sealing members receive an outer shock, they cannot sufficiently absorb the shock, so that they are distorted or gaps are created, and thus, the refrigerant correspondingly leaks out. Further, as for sealing members of propylene-based (EPDM) rubber, permeation is caused by CO2 refrigerant's characteristics, so that the refrigerant leaks out regardless of the environments.
The present invention is designed to overcome the above problems, it is an object of the invention to provide a pipe connecting structure that bears high pressure, keeps air tightness without changes in quality or deformation of a sealing member at low and high temperatures, and prevents leakage of a refrigerant by preventing permeation of CO2 in a refrigerating cycle system using CO2 refrigerant.